United Airlines Mileage Plus has announced that accounts that are inactive for 18 months will expire starting at the end of this year. Mileage Plus accounts with no activity since July 1, 2006 will have associated miles expire on Dec. 31, 2007. The previous policy allowed three years of validity. There are several ways you can save your miles: fly on United or one of its partner airlines, use or sign up for a Mileage Plus visa credit or debit card, purchase products or services from the airline’s travel and retail partners, use miles by redeeming for an award ticket or use miles for merchandise, hotel stays and dining, transfer miles to another Mileage Plus member or donate miles to the Mileage Plus Charity Miles program.

We can’t say we’re surprised by this move by United. Airlines have been known to follow the lead bird on most of these changes and some fairly big birds have recently made changes to their expiration policies (US Airways and Delta to name two). To United’s credit, they chose to announce the change in plenty of time for members to hear of the changes and make the necessary moves to save their miles. One of the easiest ways to keep the account active is to earn miles through United’s grocerymiles.com program (earn 125 miles for every $250 you spend on groceries) or you can spend as little as 500 miles for a magazine subscription. Still, we’re sure some Mileage Plus members will be taken off guard come Dec. 31, and there is no way to get their miles back once they’re gone.

On another note — to all of you mileage junkies out there — your hoarding days are numbered. Because of the literally billions of miles floating on the books of airlines, they are one-by-one deciding to do something about the miles before they come crashing down on them when baby boomers all start cashing in their miles to fund their golden travel years.